Process for preparing odorless mineral spirits by treating with acid followed by an oxidation inhibitor and then alkali



Allen E. Brehm and Theodore B. Tom, Griffith, Ind., assignors'toStandard Oil Company, Chicago, 11]., a corporation of IndianaApplication April 21, 1954, Serial No. 424,709

11 Claims. (Cl. 196-38) This is a continuation-in-part of our co-pendingapplication, Serial No. 349,892, filed April 20, 1953.

This invention relates to odorless mineral spirits. More particularlythe invention relates to solvent naphthas such as painters naphtha,which naphthas must havea minimum of the so-called naphtha odor.

Petroleum naphthas have been used for many years in the paint andvarnish industry as solvents. More recently petroleum naphthas are beingused in the syntheticresin industry as solvents. The primary objectionto the use of petroleum naphthas in these fields has been the odor ofthe naphtha. Naphthas that are essentially free of sulfur compoundsstill possess a characteristic parafiin odor. Continuous efforts havebeen made by the petroleum industry toward the production of a so-calledodorless mineral spirit for use as a solvent in the paint, varnish andresin trades.

An object of the invention is the production of an essentially odorlessand non-corrosive mineral spirit suitable for use in the paint, varnishand resin trades. Another object isthe preparation of an odorless andnon-corrosive naphtha derived from pertoleum hydrocarbons. A particularobject is an odorless mineral spirit derived from a synthetic mixture ofparaffinic hydrocarbons derived from petroleum conversion processes. Aspecific object is the production of an odorless andnon-corrosive-naphtha by acid refining of a fraction boiling betweenabout 325 and 425 F. that has been derived from the acid-catalyzedalkylation of butenes and isobutane. Other objects will become apparentin the course of the detailed description of the invention.

Mineral spirits having an odor-quality suitable for use as a solventparticularly in the paint, varnish and resin trades, are produced by aprocess comprising (1) treating a feed naphtha boiling between about 325and 425 F.'

that has been derived from hydrocarbons containing from 3 to carbonatoms, which feed is characterized by being essentially free of olefinsand aromatic hydrocarbons and elemental sulfur, with an eifective amountof sulfuric acid having a concentration of between about 90 and 100weight percent, (2) separating acid sludge from treated naphtha, (3)rain-washing said treated naphtha with liq-- uid water to removesubstantially all of the occluded-acidsludge particles therefrom, (4)separating rain-wash water from rain-washed naphtha, (5) intimatelycontacting said naphtha from step (4) with liquid water, (6) separatingWater from washed naphtha, (7) contacting said washed naphtha with anaqueous alkaline solution to essentially" neutralize said washednaphtha, (8) separating aqueous alkaline solution from an essentiallyneutral naphtha, (9) water washing said neutralized naphtha and (10)removing occluded aqueous alkaline solution from said neutralizednaphtha, wherein to the rain-washed naphtha of step 4-there is added anefiective amount of an oil soluble: aqueous-caustic insoluble oxidationinhibitor selected from. 70

the class of phenylene diamines and polyalkylphenols prior";

to the water washing'of step 5. Preferably, the oxidation 0 UnitedStates Patent inhibitor is added in an amount between about 6 and 10lbs. per 1000 bbls. (42 gal.) of naphtha.

The feed to the process of this invention is composed essentially of amixture of paraffinic and isoparatlinic hydrocarbons, i. e., isessentially free of olefins and aromatic hydrocarbons. Very smallamounts of organic sulfur compounds may be present. The feed must beessentially free of hydrogen sulfide and elemental sulfur.

The most suitable feed to the process is derived from hydrocarbonscontaining from 3 to 5 carbon atoms, which hydrocarbons have interactedto produce a mixture of essentiallly paraffinic and isoparafiinichydrocarbons of the proper boiling range for the desired solventnaphtha. In general the solvent naphtha should boil between about 325and 425 F. and preferably between about 350 and 400 F. A lower boilingpoint may be acceptable for some uses.

The mixture of hydrocarbons that are a suitable source for the feed tothe process is derived by alkylation of an olefin containing from 3 to 5carbon atoms with an isoparafiin containing from 4 to 5 carbon atoms, i.e., the feed naphtha maybe derived from the product of an alkylationreaction between an olefin selected from the class consisting ofpropene, butenes and pentenes and an isoparafiin selected from the classconsisting of isobutane' and isopentane.

Another'suitable source of feed naphtha to the process is a mixture ofhydrocarbons obtained by the polymerization of olefins containing from 3to 5 carbon atoms and the hydrogenation of the polymericmate'rials toform a mixture of essentially parafiinic and isoparafiinic hydrocarbons,i. e., thefeed naphtha may be derived from the hydrogenated product ofthe polymerization of an olefin.

' refining operations. .Typical acid catalysts are liquid hydrogenfluoride and sulfuric acid. Another example of a process for thepreparation of a suitable feed is the hydrocodimer derived from thepolymerization of a refinery propene and butene stream over a supportedphosphoric acid catalyst to form a broad boiling range unsaturatedliquid product; this unsaturated product is hydrogenated inthepresenceof acatalyst to produce an essentially saturated broadboiling product commonly known as hydrocodimer.

The preferred feed to the process of this invention is.

derived from the heavy alkylate fraction of a cold-acid alkylationprocess utilizing petroleum'refinery butenes and isobutane asthe feed tothe alkylation reaction. This material is essentially free of olefinsand contains only a very minor amount of organic sulfur compounds.

The detailed description of the process of this invention is made inconjunction with the annexed drawing, which drawingforms a part of thisspecification. The drawing shows in schematic and figurative form apreferred method of carrying out the process. Many details of equipment.have beenomitted as these may be readily supplied by those skilled inthis art.

In the drawing a heavy alkylate derived from the sul furic acidalkylation of refinery butenes and isobutanewhich boils between about325 and 600 F. is passed vfrom source 11 by way-of line 12 intofractionator l3.

Fractionator 13' isprovided with an internal heat ex ch anger l l and.with :astripping medium distributor 16; In this embodiment fractionator13 is operated with the use of Steamstripping; steam from source 17 is:passed .byv way of line 18 into distributor means 16, which means 16 ispositioned near the bottom of fractionator 13. hr

stead of using a stripping medium such as steam, com parable results canbe obtainedby operating fractionator 13 under vacuum. A high boilingbottoms fraction is withdrawn from fractionator 13 and is passed tostorage not shown by way of line 19.

An overhead fraction having a maximum ASTM boiling point of about 400 F.is withdrawn along with steam by way of line 21. The overhead naphthaand steam are condensed by means of heat exchanger 22 and the condensateis passed into line 23.

It has been found that the presence of elemental sulfur in the naphthafeed to the acid treating step of the process has an extremelydeleterious eltect on the quality of the solvent naphtha. Solventnaphtha is required to be substantially non-corrosive to the copperstrip test. The organic sulfur compounds normally present in thealkylate decompose to some extent in the distillation step to producehydrogen sulfide. This hydrogen sulfide is oxidized by free-oxygen onexposure to the atmosphere, e. g., in a storage tank, to form elementalsulfur. In general the H28 containing naphtha may be exposed tofree-oxygen for as much as four hours before deleterious amounts ofelemental sulfur are formed. In order to eliminate the formation ofelemental sulfur the H28 present in the naphtha in line 23 isneutralized by the injection of aqueous caustic. solution from source 26and line 27. Herein a weight percent aqueous NaOH solution is used.

The combined stream of naphtha, condensed steam and aqueous causticsolution is passed into mixer 28 .wherein intimate contacting takesplace. Mixer 28 may be any form of apparatus provided for intimatecontacting such as knothole mixer or a tank provided with a stirrer.From mixer 28 the mixture is passed by way of line 29 into separator 31.From separator 31 the lower aqueous phase is passed by way of line 32 towaste caustic disposal.

Feed naphtha essentially free of H28 and elemental sulfur is withdrawnby separator 31 and is passed by way of line 33 into agitator 34.Agitator 34 is a cone-bottomed contacting vessel, provided with a roof,of the type Widely used in the petroleum industry. Agitator 34 isprovided with various lines for introducing liquid and gaseous materialsinto the vessel and also meansfor withdrawing materials from the tip ofthe cone. In this particular agitator a distributor means 36 and valvedline 37 are provided near the top of the vessel.

For clarity of presentation the process is depicted in the drawing astaking place in a plurality of agitators 34a, 34b, 34c and 34d. Thesealphabetically designated agitators are shown by meansof broken lines.This has been done in order to indicate that agitators 34a34d do notactually exist in the process. The entire processing of the feed naphthafrom line 33 actually occurs in a single agitator 34. For clarity eachdistinctly different individual operation has been presented as thoughit occurred in a difierent agitator.

Returning to the first step in the process proper, feed naphtha. fromline 33 is introduced into agitator 34 until the desired amount ofnaphtha is present. Sulfuric acid from source 41 is passed by way ofline 42 into agitator 34. The sulfuric arid must have a concentrationbetween about 90 and 100 weight percent and must be used in at least aneffective amount to produce the desired odorless naphtha product.Excessive usage of sulfuric acid should be avoided. In generalbetweenabout 5 and lbs. of sulfuric acid should be used per barrel of feednaphtha. In order to produce the highest odor-quality solventnaphtha,ythe sulfuric acid should be either white acid derived from S02or the so-called black acid derived fromthe processing of refinery wasteacids and acid sludges. It is preferred to use sulfuric acid having aconcentration between about 96 and 1.00 weight percent. The amount ofacid used will vary with the type of feed naphtha charged to theprocess. v l

In this embodiment 12 lbs. of 965% black acid are used per barrel offeed naphtha (herein 42-ga1lon barrels are meant). The acid and naphthain agitator 34 are thoroughly agitated by means of compressed airintroduced from source 46 by way of valved line 47 into a lower portionof agitator 34. The agitation is continued until it is believed thereaction has been completed.

After the completion of the air agitation the contents of agitator 34are permitted to settle into an acid sludge phase and a treated naphthaphase. The lower layer of acid sludge is withdrawn by way of valved line49 and is sent to acid recovery means not shown.

It may be desirable to carry out the acid treating in more than onestage. Thus a portion of the acid may be placed in the agitator with thenaphtha, the contacting carried out and acid sludge separated. Then theremainder of the acid may be used to treat the once-treated naphtha.This multiple dump procedure is particularly useful when quite largeamounts of acid are being used.

The treated naphtha contains entrained sludge particles as well asdissolved acidic materials. It has been found that the entrained sludgeparticles, i. e., pepper sludge, readily hydrolyze on contact with waterto produce naphtha-soluble materials which impart an undesirable odor tothe product naphtha. The pepper sludge is removed from the treatednaphtha by means of a rain-wash procedure.

In this procedure. a gentle drizzle of liquid water, from source 51 andline 37, is provided by distributor 36. This rain causes droplets ofwater to fiow through the pool of treated naphtha without agitating thebody of treated naphtha. The droplets wash out of the treated naphtha,the pepper sludge and also wash from the wall of agitator 34 adheringsludge particles. The pool of treated naphtha in the agitator ismaintained in a relatively static position except for the gentle rise inlevel as a lower layer of rainwash water is formed in the bottom of theagitator. (No agitation air is introduced into agitator 34 during therainwashing procedure.)

Suflicient rain-wash water must be introduced into the agitator toremove substantially all the occluded-acid sludge particles from thetreated naptha. In the case of a well settled treated naphtha, theamount of water may be between about 5 and volume percent based ontreated naphtha. Better results are obtained by the used of two rainwashes, i. e., the treated naphtha is rain washed once and the rain-washwater withdrawn from the agitator and the rain-washed naphtha is thengiven a second rain wash followed by withdrawal of rain-wash water fromthe agitator. When operating with a plurality of rain washes arelatively small amount of water can be used in each wash. The wastewater from the rain-washing procedure is withdrawn from the agitator byway of valved line 49.

The rain-washed naphtha which is now substantially free of pepper sludgeis inhibited against oxidation by the air used for agitation in thesubsequent steps by the introduction of an effective amount of anoxidation inhibitor. The oxidation inhibitor must be oil soluble. Inorder to avoid loss of the oxidation inhibitor to either the water usedin water washing or aqueous caustic used in neutralization, theoxidation inhibitor must be essentially insoluble in water and aqueouscaustic. The oxidation inhibitor is selected from a member of the classconsisting of phenylene diamines and polyalkylphenols.

The phenylene-diamine type inhibitor may be any one of those commonlyused as oxidation inhibitors in petroleumdistillates. More particularly,the alkyl substituted amines, for example.N,N-di-secondary-butylpara-phenylene diamine. However, it is understoodthat other phenylene diamine inhibitors may be employed includingN,N-di-alkyl-p-phenylene diamines in which the alkyl groups contain from1 to about 12 carbon atoms including such compounds asN,N-di-iso-propyl-pphenylene diamine, N,N-di-amyl-p-phenylene diamine,

.N,N-di-hexyl-p-phenylene diamine, etc., as well as those in which thealkyl groups are different as, for example, in such compounds asN-prOpyl'N butyI-p-phcnylene 'diamine, N-butyl-N-amyl-p-phenylenediarnine, N-hexyl-N',-octyl-p-phenylene diamine, etc.

The amount of phenylene diamine inhibitor utilized in the process willvary somewhat with the type of rawnaphtha charged and also with theoperating conditions. In general the phenylene diamine inhibitor usagewill be at least about 4 pounds per 1000 barrels (42 gal.) ofrawnaphtha. Amounts as much as 20 pounds or more may be used in someinstances. Excessive usage has no harmful effect; however, it isuneconomic. It is preferred to use between about 6 and 10 pounds ofphenylene diamine inhibitor per 1000 barrels (42 gal.) of rawnaphtha.

The polyalkylphenol oxidation inhibitor may be any one of the commonlyknown members of this class which are sufiiciently oil soluble andessentially insoluble in water or aqueous caustic. In general thesepolyalkylphenols contain at least two alkyl groups; at least 7 carbonatoms are present as members of the substituent alkyl groups. Examplesof the polyalkylphenols useful in'this invention are di-t-butylphenol,di-amylphenol, di-t-butylmethylphenol, di-sec-butylmethylphenol,tri-isopropylphenol, tri-t-butylphenol and tri-t-amylphenol.

The amounts of the polyalkylphenol inhibitor utilized in the process ofthe invention are, in general, the same as that for the phenylenediaminetype inhibitors. That is, between about 4 and about 20 pounds per 1000barrels (42 gal.) of raw-naphtha and preferably between about 6 and 10pounds. Herein antioxidant is introduced by way of line 52 intorain-washed naphtha. Seven pounds per llOOO barrels of naphtha ofdi-t-butyl-para-cresol are utilized in this embodiment.

Liquid water from source 51 is introduced by way of valved line 37 anddistributor'36 into the agitator. When the desired amount of water has,been introduced into the agitator the naphtha and water are intimatelycontacted by agitating the contents of the agitator with compressed airfrom source. 46 and valved line 47. Agitation may also be obtained by amotor diven paddle-stirrer or by recirculating the contents of theagitator through a pump. The amount of water used in this conventional.waterwashing operation should be enough to remove essentially all thepepper sludge and water-soluble acidic materials remaining in therain-washed naphtha. The amount of water may be between about and 100volume percent based on naphtha. At the end of the contacting time thecontents of the agitator are settled and the lower water layer iswithdrawn to waste water disposal by way of line 49.

The washed naphtha contains dissolved acidic materials which must beremoved to produce a satisfactory product naphtha. Aqueous causticsolution from source 53 is passed into the agitator by Way of line 37and distributor 36. In this example a 5 weight percent aqueous NaOHsolution is used in an amount of about volume percent based on naphtha.The naphtha and aqueous caustic'solution are thoroughly intermingled bymeans of air from source 46 and line 47. When the naphtha is essentiallyneutralized the contents of the agitator are settled and the loweraqueous layer is withdrawn to waste caustic disposal by way of valvedline 49.

It has been found that in some cases even better quality mineral spiritsare obtainable by the use of aqueous caustic solution containing watersoluble polyhydroxybenzene or alkylphenol oxidation catalysts. Ingeneral, these oxidation catalysts are the same as those useful for thepromotion of the oxidation of mercaptanjs to disulfides. Examples ofthese oxidation promoters are cresol, xylenol, amylphenol, hydroquinone,catechol, pyrogallol, gallic acid, tannic acid and tannin. The aqueouscaustic solution should contain between about'l and 3 weight percent ofthe oxidation promoter. Under some conditions it is desirable to operatewithout an oil soluble oxidation inhibitor in the oil and instead useonly 6 aqueous caustic solution containing the defined oxidationpromoter. However, it is necessary to add to the product mineral spiritsan efiective amount of an oil soluble oxidation promoter in order toavoid the formation of odor during the course of storage in ventedtanks.

The neutralized naphtha contains occluded aqueous caustic solution. Thisoccluded aqueous caustic solution is removed by a conventional waterwash. Water from source 51 is passed into the agitator by way of line 37and distributor 36. Suflicient water must be used to remove the occludedcaustic. .The water and naphtha are intimately contacted by agiationwith air from source 46 and valved line 47. The contents of the agitatorare settled and the lower water layer is passed to waste water disposalby way of valved line 49.

Product odorless mineral spirits are withdrawn from the agitator andpassed to storage for further treatment by way of valved line 49a.

Normally the slight haze present in the product naphtha disappears instorage. However, this haze can be removed by passing the hazy naphthathrough a coalescer filled with fiberglass packing or rock saltgranules.

All the various steps described in the above embodiment are normallycarried out at the temperature of the water available for the washingoperations. Although normally the acid treating is so mild thatexcessive temperature rise does not occur, with some types of feed andvery heavy acid usages, it may be desirable to cool the contents ofagitator 34 by means of an internal heat exchanger not shown.

The odor quality of product solvent naphtha is determined by astandardized odor evaluation procedure. In this procedure a solventnaphtha of about ordinary commercial odor quality has been assigned anarbitrary odor value of 100. Other naphthas are compared to thisstandard naphtha by the following procedure. The unknown naphtha issmelled by each of twelve sensitive and experienced individuals; eachmember of this odor panel assigns the unknown naphtha a point value ascompared to the standard naphtha. The odor-quality of the unknownnaphtha is determined as the arithmetical average of the numerical valueassigned to the naphtha by the individual members of the panel. It hasbeen found that quite accurate reproducibility is obtainable in thispanel odor evaluation and theodor panel can check an unknown naphthawithin :1 unit.

The corrosivity of the product mineral spirits was determined by theBolt copper strip technique. This method of determining corrosion isdescribed in the August 9, 1947, issue of the Oil and Gas Journal. Ingeneral, the technique is very similar to that of the ASTM D-235 methodexcept that a number is assigned to the strip based on a standard. Inthis method, the number zero is assigned to a perfect strip, i."e., oneequal in appearance to the strip prior to having undergone the test. Thehigher the number assigned to the strip after the test, the morecorrosive the oil.

The results obtainable by the process of this invention and byconventional procedures are illustrated below.

In all experimental runs the feed naphtha was derived from a heavyalkylate that had been produced by the sulfuric acid-catalyzedalkylation of a refinery butene-butane stream. The heavy alkylate wassteam distilled, taking overhead about of the charge. The overheadfraction contained H28 and was treated with 5% aqueous NaOH solution toneutralize the H28. Tests indicated that this feed naphtha contained nodetectable amounts of elemental sulfur.

' The ASTM distillation, API gravity and sulfur content of the heavyalkylate charged to thesteam distillation, the feed naphtha whichcorresponds to about 70% of the heavy alkylate and a product odorlessmineral spirits ob-' tained by the treatmentof this feed naphthaaccording to the process of this invention are presented in Table Ibelow:

Test A In this run the feed naphtha was treated in one dump with 10lbs./bbl. of 98% refinery black acid and the acid sludge withdrawn. Thetreated naphtha was given two rain washes using 50 volume percent ofwater in each rain wash. The rain-washed naphtha was given aconventional water wash using volume percent of water. The washednaphtha was then neutralized by contacting it with 5 volume percent ofan aqueous solution containing 5 weight percent of NaOI-I. The neutralnaphtha was given a final water wash using 5 volume percent of water.

Test 8 To a sample of mineral spirits produced by the method of Test Adi-t-butyl-para-cresol was added, equivalent to 5 lbs. per 1000 bbls.(42 gal.) of the mineral spirits.

Test C In this test a sample of the feed naphtha was sweetened accordingto the procedure of Test A, except that to the rain-washed naphtha therewas added di-t-butyl-paracresol, equivalent to 5 lbs. per 1000 bbls. (42gal.) of naphtha prior to completing the treating as described in TestA.

The product mineral spirts from Tests A-C were evaluated by the odorpanel ,and also tested for corrosion to copper by the Bolt technique.The results of these tests are set out in Table II below:

TABLE II Odor- Copper Mineral Spirits Intensity Strip Reading Test A 803 Test B 80 1 Test C 73 t) The foregoing data showthat a superiorproduct is obtained by 'the process of this invention. Furthermore,these data show that, surprisingly enough, an oil which is substantiallyfree of'organic sulfur compounds can have a bad copper strip. It isbelieved that peroxides formed in the oil during the air blowing or byoxidation carried into the process dissolved in water and aqueouscaustic are responisble for this corrosivity to copper.

This theory is supported by the improvement in corrosivity by thepresence of the oxidation inhibitor in the oil during the. testprocedure. The data clearly show that superior quality oil is obtainableby introducing and maintaining in the naphtha oil soluble oxidationinhibitor subsequent to the acid treating operation.

Thus having described the invention, what is claimed is:

1. In the process for the production of an odorless mineral spirit whichcomprises (1) treating a feed naphtha boiling between about 325 and 425F. that has been derived from hydrocarbons containing from 3 to 5 carbonatoms, which feed is characterized by being essentially free of olefinsand aromatic hydrocarbons and elemental sulfur, with between about 5 and25 lbs./bbl. of free naphtha of sulfuric acid having a concentration ofbetween about and weight percent, (2) separating acid sludge fromtreated naphtha, (3) rain-washing said treated naphtha with liquid Waterto remove substantially all of the occluded-acid sludge particlestherefrom, (4) separating rain-wash water from rain-washed naphtha, (5)intimately contacting said naphtha from step (4) with liquid water, (6)separating water from washed naphtha, (7) contacting said washed naphthawith an aqueous alkaline solution to essentially neutralize said washednaphtha, (8) separating aqueous alkaline solution from an essentiallyneutral naphtha, (9) water washing said neutralized naphtha and (10)removing occluded aqueous alkaline solution from said neutralizednaphtha, the improvement which comprises introducing into therain-washed naphtha from step (4) an etfective amount of an oil solubleand essentially water and aqueous caustic insoluble oxidation inhibitorfrom the class consisting of phenylene diamines and polyalkylphenols.

2. The improvement of claim 1 wherein said phenylene ,diamine inhibitorconsists of an N,N-di-alkyl-p-phenylene diamine, wherein the alkylgroups contain from 1 to 12 carbon atoms per molecule.

3. The improvement of claim 2 wherein said diamine isN,N-disecondary-hutyl-para-phenylene diamine.

4. The improvement of claim 1 wherein the polyalkylphenol contains atotal of at least 7 substitutent carbon atoms.

5. The process of claim 4 wherein said phenol is 2,6-di-t-butyl-4-methylphenol.

6. The process of claim 4 wherein said phenol is trit-butylphenol.

7. The process of claim 1. wherein said inhibitor is added in an amountbetween about 4 and 20 lbs. per 1000 bbls. (42 gal.) of raw-naphtha.

8. In the process for producing an odorless naphtha, which processcomprises (a) distilling an alkylate derived from the acid-catalyzedreaction of an olefin selected from the class consisting of propene,butene and 'pentene with isobutane to produce a feed naphtha distillingbetween about 325 and 425 F., which feed naphtha is essentially free ofelemental sulfur, (b) treating said feed naphtha with between about 5and 25 lbs. of sulfuric acid having a concentration of between about 96and 100 weight percent and separating acid sludge from treated naphtha,(c) removing substantially all of the occluded-acid sludge particlesfrom said treated naphtha by gently flowing drops of Water through arelatively static pool of said treated naphtha and separating rainwashwater from washed naphtha, (d) intimately contacting said washed naphthawith liquid Water and separating an aqueous phase from a naphthacontaining essentially only dissolved acidic materials, (e) neutralizingthe naphtha from step (d) by contacting said naphtha with an aqueousalkaline solution and separating an aqueous phase from a naphtha phaseand (f) removing entrained aqueous alkaline solution from the naphthaphase of step (e), the improvement wherein to the rainwashed naphtha ofstep (c) there is added between about 4 and about 20 lbs. per 1000 bbls.of rawnaphtha, an oxidation inhibitor selected from the class consistingof N,N'-di-alkyl-para-phenylene diamines containing from 1 to 12 carbonatoms in said alkyl groups and polyalkylphenols containing at least 7substituent carbon atoms.

9. The process of claim 8 wherein said oxidation inhibitor is added inan amount between about 6 and 10 lbs. per 1000 barrels (42 gal.) ofraw-naphtha.

10. The process of claim 8 wherein said inhibitor isN,N-di-sec-butyl-para-phenylene diamine.

11. The process of claim 8 wherein said inhibitor is2,6-di-t-butyl-4-rnethylphenol.

References Cited in the file of this patent UNITED STATES PATENTS LeslieJuly 15, Hufi Mar. 25, Alspaugh Mar. 26, Browder May 8, Tom et a1. Nov.2,

1. IN THE PROCESS FOR THE PRODUCTION OF AN ODORLESS MINERAL SPIRIT WHICHCOMPRISES (1) TREATING A FEED NAPHTHA BOILING BETWEEN ABOUT 325* AND425* F. THAT HAS BEEN DERIVED FROM HYDROCARBONS CONTAINING FROM 3 TO 5CARBON ATOMS, WHICH FEED IS CHARACTERIZED BY BEING ESSENTIALLY FREE OFOLEFINS AND AROMATIC HYDROCARBONS ELEMENTAL SULFUR, WITH BETWEEN ABOUT 5AND 25 LBS./BBL. OF FREE NAPHTHA OF SULFURIC ACID HAVING A CONCENTRATIONOF BETWEEN ABOUT 90 AND 100 WEIGHT PERCENT, (2) SEPARATING ACID SLUDGEFROM TREATED NAPHTHA, (3) RAIN-WASHING SAID TREATED NAPHTHA WITH LIQUIDWATER TO REMOVE SUBSTANTIALLY ALL OF THE OCCULUDED-ACID SLUDGE PARTICLESTHEREFROM, (4) SEPARATING RAIN-WASH WATER FROM RAIN-WASHED NAPHTHA, (5)INTIMATELY CONTACTING SAID WASHED NAPHTHA FROM STEP (4) WITH LIQUIDWATER, (6) SEPARATING WATER FROM WASHED NAPHTHA, (7) CONTACTING SAIDWASHED NAPHTHA WITH AN AQUEOUS ALKALINE SOLUTION TO ESSENTIALLYNEUTRALIZE SAID WASHED NAPHTHA, (8) SEPARATING AQUEOUS ALKALINE SOLUTIONFROM AN ESSENTIALLY NEUTRAL NAPHTHA, (9) WATER WASHING SAID NEUTRALIZEDNAPHTHA AND (10) REMOVING OCCLUDED AQUEOUS ALKALINE SOLUTION FROM SAIDNEUTRALIZED NAPHTHA, THE IMPROVEMENT WHICH COMPRISES INTRODUCING INTOTHE RAIN-WASHED NAPHTHA FROM STEP (4) AN EFFECTIVE AMOUNT OF AN OILSOLUBLE AND ESSENTIALLY WATER AND AQUEOUS CAUSTIC INSOLUBLE OXIDATIONINHIBITOR FROM THE CLASS CONSISTING OF PHENYLENE DIAMINES ANDPOLYALKYLPHENOLS.